As the two candidates for John Kerry’s former Senate seat in Massachusetts blaze through their final full day of campaigning Monday, a single question hangs over the pre-election barnstorming: When the polls open Tuesday morning, who will show up?

While nearly all of the polling in the race to date has shown Democrat Edward Markey leading Republican Gabriel Gomez, the margin has fluctuated, suggesting that political scientists are still having trouble pinning down just who qualifies as a “likely voter” in this off-year, off-season election.

In a poll released Sunday by the Western New England University Polling Institute, for instance, 23 percent of voters with a candidate preference said they might still change their mind, compared with only 9 percent at the same point in the 2012 Senate race here.

Political scientists attribute the low interest in the race to everything from the season and a glut of other headline-grabbing news – including the Boston Bruins’ fight for the Stanley Cup and the much-awaited trial of reputed Boston mobster James “Whitey” Bulger – to a generalized political exhaustion in the state.

This is the fourth Senate election in Massachusetts in the past five years, and it’s been only seven months since voters here elected their last senator, Democrat Elizabeth Warren. Nearly as soon as this campaign ends, the winner will begin to regroup for his reelection run in 2014. What’s more, if Markey becomes senator, his congressional seat will fall open, triggering yet another special election to select his replacement.

Adding to low interest in the race has been its brisk pace. With less than two months from the primaries to the general election, neither candidate has had a great deal of time to orient their image or messaging. And most voters do not appear to be giving the candidates a great deal of their time.

Less than a quarter of likely voters said they watched the most recent debate between the two candidates, according to a Suffolk University poll released Monday, and only 42 percent of registered voters say they are very interested in the race, according to the Western New England University Polling Institute.

As this campaign entered its final hours, the two candidates spent a sweltering weekend zig-zagging across the state to meet voters and rouse their legions of canvassers and phone-bankers. Markey circled Boston and its suburbs, appearing alongside Senator Warren, Vice President Joe Biden, former Gov. Michael Dukakis, and Vicki Kennedy, the widow of former Sen. Edward Kennedy. They’re the latest in a long list of Democratic A-listers to appear for Markey on the campaign trail, including both Barack and Michelle Obama and Bill Clinton.

Gomez, meanwhile, continued his habit this weekend of meeting with voters in small, informal groups, logging 16 separate stops across the state on Saturday on Sunday, including a 5k run, an ice cream shop, and a minor league baseball game. The businessman and former Navy SEAL, who has never held political office, has made these grass-roots visits the centerpiece of his campaign, logging Bruins watch parties, family barbecues, and meals at local sandwich shops nearly every day of his campaign.

Scott Brown, the Republican who swept to a surprise victory in the last special Senate election in Massachusetts, in 2010, will appear with Gomez at a rally Monday evening. It will be his first major foray into the race.